PROJECT SUMMARY/ ABSTRACT Patients with Li-Fraumeni syndrome are predisposed to cancer resulting from germline mutations in the tumor suppressor, p53. Inheritance of mutations in p53 occurs in an autosomal dominant pattern and results in an increased lifetime risk for developing multiple malignancies with a significant likelihood of early onset. Although prior studies using mouse knockouts have demonstrated that p53 plays a role in kidney formation, developmental kidney anomalies have not been associated with p53 mutations seen in Li-Fraumeni patients. Preliminary MRI data indicate that these patients have a higher incidence of urogenital anomalies than the general population. Thus, the goal of this proposal is to utilize Xenopus embryos to assess p53's fundamental role in kidney development and to generate animal models to determine whether p53 mutations seen in Li- Fraumeni patients result in renal anomalies. The proposed experiments will test the hypothesis that the p53 dysfunction in Li-Fraumeni patients results in kidney developmental anomalies. The hypothesis will be tested through the following aims: Aim 1. Evaluate kidney defects resulting from p53 disruption in Xenopus embryos. Previous studies showed that p53-null mouse embryos have developmental kidney defects, including duplex ureter and renal hypoplasia. Preliminary data indicate that similar nephric developmental defects are also present when p53 levels are reduced in the kidneys of Xenopus embryos, a useful model for dissecting the mechanisms that contribute to developmental defects. To set the foundation for future analysis of the molecular mechanism of p53 activity, the hypothesis that p53 regulates nephron differentiation will be tested in the Xenopus kidney. This will be achieved through novel strategies targeting CRISPR knockout of p53 to the Xenopus kidney, quantitation of pronephric developmental features, and analysis of expression of markers of kidney development. Aim 2. Determine whether p53 mutations seen in Li-Fraumeni patients result in renal anomalies. Preliminary MRI data indicate that Li-Fraumeni patients have an increased incidence of urogenital anomalies. The hypothesis that the p53 mutations that cause Li-Fraumeni syndrome result in disruption of Xenopus nephron development will be tested, thereby generating animal models of Li-Fraumeni kidney anomalies for future research. Given that the p53 mutations from these patients are anticipated to act through gain-of-function mechanisms, this will be carried out by targeting expression of the p53 alterations to the Xenopus kidney, studies that would be difficult and time-prohibitive in other models. Overall, the experiments proposed in this application will facilitate our understanding of how p53 affects nephron formation generally and how Li-Fraumeni patient mutations in p53 may disrupt this process.